Bathothauma lyromma Chun, 1906

Bathothauma contains one recognized species. Voss, et al. (1992), however, suggest that four species may exist.

Introduction

Bathothauma lyromma is one of the more highly modified cranchiids. The paralarval stage reaches a very large size (ca. 10 cm ML) and possesses very long eye stalks and has a very long brachial pillar. Both are resorbed in the subadult. The adult reaches 20 cm ML (Nesis, 1982). This species is circumglobal in distribution from tropical to high latitudes (Voss, 1980).

Diagnosis

A taonin ...

• with widely separated paddle-shaped fins.

Characteristics

1. Tentacles
   1. Tentacular club with suckers only.
   2. Tentacular stalk with two series of suckers and pads proximally, four series near club forming elongate carpal group.
2. Funnel
   1. Funnel valve absent.
   2. Funnel organ with inverted V-shaped dorsal pad
      
      
3. Mantle
   1. Tubercles absent (or virtually absent) from funnel-mantle fusion.
      
      
4. Fins
   1. Fins paddle-shaped, subterminal.
   2. Fins widely separated (insert on lateral, expanded ends of transverse extensions of posterior end of gladius).*
      
      
5. Photophores
   1. One on each eye.**
   2. Arm-tip organs of adult females unknown.

*Within Cranchiidae, unique to this genus.
**Unusual feature within Cranchiidae; shared only with Helicocranchia.

Comments

Characteristics above are from Voss (1980).

Life History

The paralarva is very distinctive with extremely long eye-stalks, a long brachial pillar, widely separated fins and an unusual chromatophore pattern.

image info image info

Figure. Left - Dorsal view of a large paralarva (ca. 50 mm ML) B. lyromma, Hawaiian waters. Photograph by R. Young. Right - Ventral and dorsal views of a small paralarva (ca. 5 mm ML) of B. lyromma, Hawaiian waters. The drawings emphasize the eye-rostrum by showing the eyes in different orientations: The left eye is seen in a side view and the right eye in either a ventral view (left drawing) or a dorsal view (right drawing). Drawings by R. Young. The scale bar is 1 mm.

Distribution

Vertical distribution

The vertical distribution of B. lyromma off Hawaii exhibits a clear ontogenetic descent. No adults were taken in this study but they probably occur at depths greater than 1000 m.

image info

Figure. Vertical distribution chart of B. lyromma, Hawaiian waters. Captures were made with both open and opening/closing trawls. Bars- fishing depth-range of opening/closing trawl. Circle- Modal fishing depth for either trawl. Blue-filled circles- Night captures. Yellow-filled circles- Day capture. Chart modified from Young (1978).

Geographical distribution

The genus is found circumglobally in tropical and subtropical waters except for an apparent absence from subtropical waters of the South Atlantic. It also extends into temperate waters in the northeastern Atlantic and South Pacific (Voss, 1992).

References

Chun, C. 1910. Die Cephalopoden. Oegopsida. Wissenschaftliche Ergebnisse der Deutschen Tiefsee-Expedition, "Valdivia" 1898-1899, 18: 1-522 + Atlas.

Voss, N. A. 1980. A generic revision of the Cranchiidae (Cephalopoda; Oegopsida). Bull. Mar. Sci., 30: 365-412.

Voss N. A., S. J. Stephen and Zh. Dong 1992. Family Cranchiidae Prosch, 1849. Smithson. Contr. Zool., 513: 187-210.

Young, R. E. (1978). Vertical distribution and photosensitive vesicles of pelagic cephalopods from Hawaiian waters. Fish. Bull., 76: 583-615.